The present invention relates to a cylinder head of an engine in which variable valve actuating units are disposed on an intake side thereof.
There have been proposed engine cylinder head reinforcement constructions for increasing the rigidity of a cylinder head of an engine so as to withstand explosions occurred within combustion chambers.
In reinforcement constructions of this type, injector holding bosses adapted to hold injectors installed individually for combustion chambers are connected to each other in a longitudinal direction (a direction in which the combustion chambers are aligned) of a cylinder head, and the injector holding bosses lying at both ends are connected to an outer circumferential wall portion of the cylinder head, whereby a reinforcement wall portion is formed where the bosses and the outer circumferential wall portion are connected integrally.
Furthermore, on an intake side of the cylinder head, intake camshaft supporting portions which support thereon an intake camshaft disposed on the intake side and journals of the same camshaft extend in an intake-to-exhaust direction (a direction which intersects the longitudinal direction of the cylinder head at right angles) and are connected to the reinforcement wall portion and the outer circumferential wall portion, whereby reinforcement wall portions are formed. Similarly, also on an exhaust side, exhaust camshaft supporting portions are connected to the reinforcement wall portion made by the injector holding boss portions and the outer circumferential wall portion, whereby reinforcement wall portions are formed.
By this configuration, the rigidity of the cylinder head is increased by the reinforcement wall portions which intersect each other, and additionally, a balance in rigidity is made to be maintained between the intake side and the exhaust side (refer, for example, to JP-A-5-86813).
On the other hand, there are some engines which include variable valve actuating units for adjusting the operations of intake valves in accordance with the running conditions of a vehicle.
For variable valve actuating units to be installed, boss portions where the variable valve actuating units are installed are formed on an intake side of a cylinder head. When the boss portions are formed on the intake side, however, the rigidity of the intake side is increased to be higher than that of an exhaust side of the cylinder head due to the boss portions so formed functioning to reinforce the part in question of the cylinder head. As a result of this, the rigidity of the intake side is made to differ from the rigidity of the exhaust side, and hence, the balance in rigidity is deteriorated.
It is not preferred that the balance in rigidity between the intake side and the exhaust side of the cylinder head is deteriorated.